Re: Need some light on using Ada or not

["Luis P. Mendes" <luislupeXXX@gmailXXX.com>]

Sun, 20 Feb 2011 19:54:30 +0000, Brian Drummond escreveu:

> On 20 Feb 2011 00:20:56 GMT, "Luis P. Mendes" <luislupeXXX@gmailXXX.com>
> wrote:
> 
>>Sat, 19 Feb 2011 13:07:58 +0000, Brian Drummond escreveu:
>> 
>>> Ada can easily bind to C libraries, it's standard and well documented.
> 
>>> C++ bindings are also possible, but with some work and (currently)
>>> some limitations.
>>> A GCC recent enough to support "-f-dump-ada-spec" will auto-generate
>>> an Ada spec from C++ sources, which will save a lot of the work.
>>
>>Would you mind giving me an example?
> 
> See below...
> 
>>Please consider the following C++ code: ===== header file
>>$ cat aleatorio.h
> 
>>===== source file
>>$ cat aleatorio.cpp
> 
>>=====
>>
>>From Ada, how can I use these h and cpp files to call, for example,
>>gerarAleatorioInteiro(0,10)?
> 
> Here is what I did.
> 
> 1)  Comment out the #includes in aleatorio.h. They are unused; enlarge
> the namespace; and are repeated in the .cpp file anyway.
> 
> Save it as aleatorio.hpp. (This forces C++-style Ada specs rather than
> C-style, which is essential to link to C++ code)
> 
> 2) Generate the specs automatically.
> /usr/gnat/bin/gcc -fdump-ada-spec aleatorio.hpp produces an automatic
> spec file
> aleatorio_hpp.ads
> -------------------------------
> with Interfaces.C; use Interfaces.C;
> 
> package aleatorio_hpp is
> 
>    procedure iniciarSemente;  -- aleatorio.hpp:8:21 pragma Import (CPP,
>    iniciarSemente, "_Z14iniciarSementev");
> 
>    function gerarAleatorio (a : int; b : int) return double;
> 	-- aleatorio.hpp:9:35
>    pragma Import (CPP, gerarAleatorio, "_Z14gerarAleatorioii");
> 
>    function gerarAleatorioInteiro (a : int; b : int) return int;
> 	-- aleatorio.hpp:10:39
>    pragma Import (CPP, gerarAleatorioInteiro,
>    "_Z21gerarAleatorioInteiroii");
> 
>    function arredondar (res : double) return int;
> 	-- aleatorio.hpp:11:26
>    pragma Import (CPP, arredondar, "_Z10arredondard");
> 
> end aleatorio_hpp;
> -------------------------------
> 
> 3) Not essential but recommended ...
> 
> Write a wrapper package to hide the C interface and C types, and to make
> the interface look like Ada: random_wrapper.ads, random_wrapper.adb.
> (This constitutes a "thick binding", while package aleatorio_h is a
> "thin binding")
> At this point you can choose what to expose to the Ada code; I have been
> selective (or lazy!)
> 
> ------------ random_wrapper.ads -------------- package random_wrapper is
>  
>    procedure initialise_seed;
>    function random_between(a,b : in Integer) return Integer;
>   
> end random_wrapper;
> ------------ random_wrapper.adb -------------- with aleatorio_hpp;
> use aleatorio_hpp;
> with Interfaces.C;
> use Interfaces.C;
> 
> package body random_wrapper is
> 
>    procedure initialise_seed is
>    begin
>       iniciarSemente;
>    end initialise_seed;
> 
>    function random_between(a,b : in Integer) return Integer is begin
>       return Integer(gerarAleatorioInteiro (int(a), int(b)));
>    end random_between;
> 
> end random_wrapper;
> ----------------------------------------------
> 
> 4)  Write your Ada program...
> ------------ random.adb ---------------------- --Random number tester
> 
> with Ada.Text_Io; 		use Ada.Text_Io;
> with Ada.Integer_Text_Io; 	use Ada.Integer_Text_Io; with 
random_wrapper;
> 	use random_wrapper;
> 
> procedure random is
> 
> begin
>    initialise_seed;
>    Put("Five random numbers");
>    New_Line;
>    for i in 1 .. 5 loop
>       Put(random_between(1,100));
>       New_Line;
>    end loop;
> end random;
> ----------------------------------------------
> 
> 5) Compile the C++ portion (more complex examples may need a Makefile)
> 
> g++ -g -m64 -c -o aleatorio.o aleatorio.cpp
> 
> 6) Build the Ada portion.
> 
> gnatmake -m64 -gnat05 -gnato -gnatwa -fstack-check -o random random.adb
> \
> 	-largs ./aleatorio.o -lstdc++
> 
> Note additional arguments "-largs ./aleatorio.o -lstdc++" to gnatlink;
> extend these if you add more C++ objects and libraries.
> 
> 7)
> Run it.
> 
> ./random
> Five random numbers
>           9
>          40
>           2
>          77
>          66

Thank you very much Brian!

I guess that this example or another one like this could be included in 
wiki or other place for newcomers.


Luis